1. Field of the Invention
The present invention relates to a device for the passage of air, in particular to a filter fan or outlet filter.
2. Description of the Related Art
For components placed in a casing which produce waste heat, it is necessary to carry away the waste heat form the casing and to control a temperature in the casing by more or less strong blowing in or sucking off of ambient air into the casing inner space by means of a fan. Computer casings are a known example for this, whereby the guiding principle is that the more cooling the better. Usually such casings are provided with a filter fan which either is continually running or which is switched on and off by a control device depending on a temperature in the casing. The filter fan is placed in a recess of a wall of the casing and fixed for example by means of screwed connections. Simultaneously corresponding air outlet slits are provided at another place of the casing for the air outlet.
Because of the electrostatic charging of the electronic structural members and components which are placed in the inside of the casing, dirt and dust particles accumulate thereon so that there can be dysfunctions of the components. In order to avoid dirt accumulation, it is known to provide in the fan an additional filter mat preferably of a knitted or needled synthetic material in order to filter out these dust and dirt particles from the air which is conveyed through the fan in a flow direction. For this purpose, a filter mat is preferably placed in flow direction of the air before the blast of the fan, whereby an intermediate space between the filter mat and the blast is closed substantially air tight against the ambient air by a basic casing and a blast support. The filter mats used for these filter fans are placed between the outer filter grid and the basic casing. The fan grid is removably connected with the basic casing by means of clamping or snap-in connections or screwed connections.
The air outlet of the device for the passage of air is covered for known fans with a grid element which either covers the outlet plainly, or shell-shaped. The air which comes out of the air outlet through the grid element into the casing moves axially or in flow direction and straight into the casing. The air must then distribute itself or an active air distribution has to take place. It is aimed at that an active air distribution can be avoided or that the air distributes itself better. Furthermore, it is possible that parts of the outcoming air flow in particular in the middle are sucked again into the passage.